While it is known to be old to optimize a control system and allow one of a plurality of operating loads having the greatest demand control the output of temperature conditioning apparatus, such as in a pneumatic system of the K. G. Kreuter et al. U.S. Pat. No. 3,338,519 and in a heating and cooling system as shown in the D. E. Zimmer et al. U.S. Pat. No. 3,933,197, the present invention is concerned with a plurality of food refrigeration display cases each of which has an evaporator connected to a refrigerator system having a plurality of compressors. Previously, the compressors were controlled off of some low pressure controller to maintain a refrigerant pressure sufficient to satisfy the load which might be imposed on the refrigeration apparatus by any one of the plurality of evaporator cases.
The present invention provides an individual control device for each evaporator of the display cases or a plurality of display cases which has an output signal indicative of the load of that particular evaporator or evaporators. A plurality of such control devices have each of their output circuits connected, through a means to select the highest demand signal, to a control panel for controlling the total operating capacity of the refrigeration compressors. Specifically, the control device controls the suction pressure of the display case by a valve in the refrigerant line from the evaporator and provides an output signal indicative of the evaporator load. The output signal of each of said control devices is connected by means of a diode to the input of a control circuit and the control signal having the greatest magnitude from the control device of the evaporator having the greatest load, controls the level of output of the plurality of refrigeration compressors by sequentially turning more or less of the compressors in an "on" operation. Such a system maintains the level of output of the refrigeration apparatuses sufficient to maintain a flow of refrigerant from the evaporator having the greatest load.
FIG. 1 is a schematic representation of the refrigeration system showing the plurality of display cases each having an evaporator to which refrigerant is delivered from a refrigeration apparatus having a plurality of refrigeration compressors.
FIG. 2 made up of FIGS. 2A, 2B and 2C are schematic showings of the control circuit providing the input circuit to which the individual signals are fed to provide an output signal for sequentially controlling the refrigeration compressors.